Feline Herpesvirus Infection

Feline herpesvirus type Ⅰ (FHV-1) is the causative agent of feline herpesvirus disease. This prevalent virus has a single identified serotype, but its virulence varies among strains and can result in acute respiratory syndrome in cats, presenting as a highly contagious upper respiratory tract disease. With an in-depth understanding of FHV-1, BioVenic is committed to providing diagnostic, preventive, and treatment development services for veterinary researchers concentrating on this virus.

Etiology

FHV-1 belongs to the family Herpesviridae, the subfamily Alphaherpesvirinae, and the genus Varicellovirus. It is an enveloped double-stranded DNA virus with an envelope. The entire virion is relatively large and has an icosahedral structure with a diameter of about 135-185 nm. The full length of the viral genome is 126-135 kb, consisting of a long unique region (UL) and a short unique region (US). The genome encodes a variety of proteins, among which the identified envelope glycoproteins include gB, gC, gD, gG, gE, gI, gH, and gL, these glycoproteins are involved in processes such as virus recognition of host cells, mediation of cell fusion, and play a huge role in induction of immunity.

Fig. 1 Negative-stained electron micrograph of FHV-1 particles.¹

Distribution

The disease was first discovered in the United States, and then Canada, the Netherlands, the United Kingdom, and other countries successively discovered the disease. At present, FHV-1 has been distributed in all countries in the world, and the infection rate in some cat populations is as high as 97%.

Susceptible Animals

FHV-1 exhibits strict host specificity, exclusively infecting cats and not affecting other animals. Cats of all breeds and ages can contract the virus, with kittens, particularly those that are unvaccinated, being highly susceptible to infection, leading to the manifestation of severe clinical symptoms.

Transmission

FHV-1 generally infects cats through the mouth, nose, and eye conjunctiva. The primary mode of transmission is direct contact with materials contaminated with FHV-1.

Pathogenesis

Following infection, FHV-1 replicates in respiratory epithelial cells and attacks the conjunctiva and cornea, causing inflammation and damage to nasal and ocular tissues. If the infectious agent is not cleared, FHV-1 can continue to invade the bones of the nose and mouth, causing facial deformities.

Signs and Symptoms

In addition to general symptoms such as fever, elevated body temperature, and depression, unwell cats primarily exhibit respiratory and ocular symptoms.

• Respiratory Symptoms
  
  • Increased discharge from the eyes and nose
  • Sneeze
  • Difficulty breathing
  • Tongue and hard palate ulcers
• Eye Symptoms
  
  • Red and swollen eyes
  • Herpetic keratitis
  • Severe dendritic ulcer

Diagnosis

The disease often presents symptoms indistinguishable from feline distemper and feline calicivirus infections, making laboratory diagnosis essential. Methods for detecting FHV-1 include virus isolation and identification, electron microscopy observation, serological testing, etc. Additionally, emerging rapid detection methods like recombinase-assisted amplification (RAA) are available. We provide immunology and molecular-based diagnostic kit development services to veterinary researchers.

• Veterinary Immunodiagnostics Development
  
  • ELISA
  • Western blot (WB)
• Veterinary Molecular Diagnostics Development
  
  • PCR
  • qPCR

Treatment

There is no specific drug for FHV-1. Treatment for FHV-1 infection is primarily focused on managing the symptoms and providing supportive care. The treatment plan may vary depending on the specific symptoms exhibited by the cat. Here is a detailed treatment plan divided into points:

• Ocular Symptoms
  
  • Topical eye medications: In cases of conjunctivitis or other ocular symptoms, topical eye medications may be prescribed. These can include antiviral ophthalmic drops such as idoxuridine, trifluridine, or cidofovir.
  • Oral antiviral medications: In severe or recurrent ocular infections, oral antiviral medications like famciclovir may be prescribed.
• Respiratory Symptoms
  
  • Symptomatic treatment: Environmental humidification, such as steam inhalation or nebulization, can help alleviate nasal congestion.
  • Supportive care: Cats with respiratory symptoms may have a decreased sense of smell, leading to a decreased appetite. In some cases, an appetite stimulant may be prescribed.
• Antibiotics
  
  • Antibiotics, such as amoxicillin and doxycycline, are also employed in the presence of upper respiratory tract infections.
• L-lysine Supplementation
  
  • L-lysine is a commonly utilized supplement for FHV-1 infections, believed to aid in inhibiting the virus.
• Hospitalization and Intensive Care
  
  • If a cat with FHV-1 infection experiences severe symptoms, more intensive treatment may be necessary, including intravenous fluid therapy, nutritional support, and oxygen therapy.
• Probiotics
  
  • Some studies have shown that supplementation with probiotics can have benefits in reducing the clinical signs of FHV-1 infection. Probiotics help support the cat's gut health and immune system.

Prognosis

The prognosis of sick cats mainly depends on the severity of symptoms and the physical condition. In general, prompt treatment helps most cats recover and lead normal lives. However, infected cats are lifelong carriers after recovery. FHV-1 is latent in the optic nerve or trigeminal nerve and can be reactivated to cause recurrent disease when the body's immunity is weakened.

Prevention and Control

Proper immunization of kittens is the most effective preventive measure. Currently, there are two commonly used types of vaccines: inactivated vaccines and live vaccines. When administered through appropriate immunization procedures, all forms of vaccines demonstrate excellent protective effects.

Good hygiene practices are paramount in preventing FHV-1 transmission. Regular cleaning of litter boxes, disinfection of shared objects, and minimizing stressors can help reduce the risk of viral spread. Isolating infected cats and providing proper care can also contribute to preventing FHV-1 outbreaks in multi-cat environments.

As a leader in the field of veterinary medicine, BioVenic is committed to advancing the understanding, prevention, and control of FHV-1 infections. Through extensive research, our dedicated team develops innovative diagnostics, vaccines, and treatment options to combat this viral disease. If you need our technical support, please feel free to contact us.

Reference

1. Sun, Heting, et al. "Isolation and identification of feline herpesvirus type 1 from a South China tiger in China." Viruses 6.3 (2014): 1004-1014.